Lubricant compositions



3,247,109 LUBRIQANT COMPOSITIGNS George J. Benoit, J12, San Anselmo, Califi, assignor to (Ihevron Research Company, a corporation of Delaware No Drawing. Filed Apr. 23, 1962, Ser. No. 189,270

2 Claims. or. 252-321 This application is a continuation-in-part of George J. Benoit, IL, US. patent application Serial No. 794,801, filed February 24, 1959, now abandoned, directed to Dialkyl Diesters of Dibasic Acids.

This invention relates to a novel lubricant composition having as the base oil a new class of dialkyl diesters of dibasic acids. More particularly, the invention is concerned with a synthetic lubricating oil composition com prising a novel class of dialkyl diesters of alkoxysuccinic acids and alkylthiosuocinic acids having superior properties.

Synthetic oils are useful in a variety of applications, including the lubricants of instruments, Weapons, optical equipment, gas turbines, etc. A combination of special properties is desirable in synthetic oils for these purposes. At high temperatures, they should not be excessively volatile in order to avoid the loss of the oil through evaporation to permit their circulation, and the provision of proper lubrication over Wide ranges of operating conditions. It is also important that the synthetic oils remain fluid at low as well as high temperatures. Good viscosity-temperature properties are likewise desirable in synthetic oils since they should be adaptable to changes in temperature conditions without extreme variations in viscosity. Suitable synthetic oils should also be stable to oxidation, particularly at high temperatures, since undesirable residues such as tars and coke will otherwise result.

It has now been found that a superior new gas turbine lubricating oil composition is provided by the composition comprising a major proportion of a synthetic lubricating oil base of the class consisting of the dialkyl diesters of alkoxysuccinates and alkylthiosuccinates in which the alkoxy and the alkylthio group contain from 1 to about 12 carbon atoms and the alkyl ester groups contain from about 4 to about 12 carbon atoms each in combination with an arylamine oxidation inhibitor and an alkylamine salt of acid alkyl esters of phosphoric acid as extreme pressure additive. Such compositions are excellent synthetic oils having special proporties which make them particularly suitable as synthetic lubricants.

The novel dialkyl diesters of alkoxysuccinic acids and alkylthiosuccinic acids according to the present invention, as described above, are characterized by unusually low freezing points compared to other types of dialkyl diesters of dibasic acids. This property shows that they are capable of remaining fluid and provide effective lubrication at low as well as high temperatures. The superior new esters of the invention also possess excellent viscosity-temperature characteristics as indicated by their high viscosity indexes. From the standpoint of oxidation stability, the novel dialkyl diesters of alkoxysuccinic acid and alkylthiosuccinic acids according to the invention are particularly desirable since they form less tar and coke under actual operating conditions than other types of dialkyl diesters of'dibasic acids.

The superior new dialkyl diesters of alkoxysuccinic acids and alkylthiosuccinic acids according to the invention have the general formula in which R and R are the same or different alkyl groups containing from about 4 to about 12 carbon atoms each, R is an alkyl group containing from 1 to about 12 carbon atoms and X is a member of the group consisting of oxygen and sulfur. The dialkyl diesters in which one of the alkyl groups is straight chain in structure and the other branched chain are particularly desirable since they are characterized by an excellent combination of high viscosity index and low pour point. Particularly preferred for present purposes are the dialkyl diesters of methoxysuccinic acid in which one of the alkyl groups is a straight chain alkyl group of from about 6 to about 10 carbon atoms and the other alkyl group is a branched chain alkyl group of from about 6 to about 10 carbon atoms.

Examples of the superior new dialkyl diesters of allroxysuccinic acid or dialkyl diesters of alkylthiosuccinic acids according to the invention include the diisooctyl diester of isooctoxysuccinic acid, the di-Z-ethylhexyl diester of 2-ethylhexoxysuccinic acid, the diisooctyl diester of n-butylthiosuccinic acid, and other similar compounds within the aforementioned general description. For our purposes, the n-octyl, 0x0 decyl diester of methoxysuccinic acid is preferred for its outstanding combination of physical properties including high viscosity index and low pour point. The oxo decyl group in this case is a typical branched chain alkyl group of 10 carbon atoms derived from oxo decyl alcohol prepared by the oxo" process from propylene triiner.

The dialkyl diesters of the alkoxysuccinic acids according to this invention are conveniently prepared by reacting an alkali metal alcoholate in aicohol (i.e., methanol) solution with a dialkyl diester of maleic acid. The alcohol, for example, methanol, adds across the double bond of the maleate ester, for example, diethyl maleate, to give the dialkyl diester of methoxysuccinic acid. This dialkyl diester is then reacted with another type of alco- 1101 such as n-octanol in an ester interchange to give the di(n-octyl)-diester of methoxysuccinic acid.

The arylamine oxidation inhibitor is employed in amounts of from 0.2 to 5%, and preferably from 0.5 to 3% by weight. Suitable arylamine oxidation inhibitors include phenyl-a-naphthylamine, diphenylamine, dioctyl diphenylarnine, phenothiazine and the like. Particularly suitable are the diarylamines which contain from about 10 to about 25 carbon atoms. For present purposes, phenothiazine is preferred.

The extreme pressure additive is employed in the amount of from 0.05 to 1%, and preferably of from 0.1 to 0.5% by weight. This compound is selected from the group consisting of alkylamine salts of acid alkyl esters of phosphoric acid and blends of said salts with acid alkyl esters of phosphoric acid in which the amine salt constitutes at least 25% by weight, the alkyl groups here referred to containing from 8 to 18 carbon atoms each. Suitable additives coming within this group are dodecylamine dodecyl acid phosphate, blends made up of fro-m 25 to 95% of dodecylamine dodecyl acid phosphate and from to 75% of dodecyl dihydrogen phosphate, octylamine dioctyl phosphate, di(decylamine)dodecyl phosphate, hexadecylamine dodecyl acid phosphate, octadecylamine dioctadecyl phosphate, and blends containing 2- ethylhexylamine 2-ethylhexyl acid phosphate and 2-ethylhexyl dihydrogen phosphate in equal proportions. A preferred extreme pressure additive is a blend made up of an alkaylamine acid alkyl phosphate with an alkyl dihydrogen phosphate, in which blend the amine salt component is present to the extent of from 25 to 95% by weight.

The synthetic lubricating oil compositions according to the invention may also contain anti-wear additives, metal deactivators, foam inhibitors, and the like.

The anti-wear additive is present in the amount of from 0.5 to 5% and is a compound selected from the group consisting of neutral aryl phosphates and neutral alkyl aryl phosphates. Representative additives coming within this grouping are triphenyl phosphate, tricresyl phosphate, buty-l diphenyl phosphate, phenyl dibutyl phosphate, benzyl dicresyl phosphate, trixylyl phosphate and diphenyl cresyl phosphate. A preferred additive of this class is tricresyl phosphate.

The metal deactivator additive, which is present in the amount of from 0.005 to 0.2%, and preferably from 0.0 1 to 0.1% by weight, is a compound selected from the group consisting of quinizarin, alizarin, purpurxanthrene, anthrarufin, and chrysazin. The preferred additive of this class is quinizarin.

As the foam inhibitor there is employed from 0.0001 to 0.02% of a di(lower alkyl)silicone polymer such as dimethyl silicone, diethyl silicone, methylethyl silicone and methylphenyl silicone. The preferred additive of this class is dimethyl silicone.

In further illustration of the invention, reference is had to the following examples. The proportions in the examples are given on a weight basis unless otherwise specified.

EXAMPLE I In this example, dioctyl methoxysuccinate was prepared. A sodium methylate solution in methanol was prepared by reacting 2.3 g. sodium (0.1 g. atom) with 160 g. methanol (5.0 moles). To this solution 172 g. diethyl maleate (1.0 mole) was added and the reactants heated to 50-60 C. for 4 hours. A mixture of 500 g. n-octanol and 500 ml. toluene was next added and the mixture distilled until all the toluene and lower boiling alcohols were removed. The pot temperature at this point was 195 C. It was then distilled under a vacuum of 3.4 mm. of mercury to a pot temperature of 220 C. This yielded a bottoms fraction of 263 g. which was filtered and treated with 5 g. of acetic acid. The stock so treated was distilled, topping at a pressure of 1 mm. of mercury, to a pot temperature of 100 C. and filtered. The analytical results and physical property data for this ester are given in the attached table.

EXAMPLE II This example illustrates the preparation of di-(2-ethylhexyl) 2-ethylhexoxysuccinate.

Sodium 2-ethylhexoxide was prepared by adding 2.3 g. (0.1 g. atom) sodium to 650 g. 2-ethylhexanol (5.0 moles). One hundred seventy-two grams diethyl maleate (1.0 mole) was added to the solution of the sodium alcoholate and the mixture heated to 5060 C. for 4 hours. Five hundred milliliters of toluene was added and the mixture subjected to distillation to a pot temperature of 200 C. Eight grams of acetic acid was next added and the mixture distilled under a pressure of 2 mm. of mercury to a pot temperature of 200 C. The bottoms was decolorized with carbon at 100 C., filtered, and topped at a pressure of 8 mm. of mercury to a pot temperature of 220 C.

4 EXAMPLE III In this example, di-n-hexyl n-hexoxysuccinate was prepared.

A solution of sodium n-hexoxide in n-hexanol was prepared as in the preceding experiments. T o 512 g. of this solution containing 0. 1 g. atom of sodium was added 172 g. diethyl maleate (1.0 mole). This mixture was heated to 5060 C. for 4 hours, cooled, and 500 ml. of toluene was added. The volatile material was removed by distilling at atmospheric pressure to a pot temperature of C. It was then neutralized with acetic acid, and decolorizing carbon was added. The mixture was distilled at a pressure of 5.0 mm. of mercury to a pot temperature of 235 C.; and the bottoms, weighing 373 g. was filtered.

EXAMPLE IV This example illustrates the preparation of mixed hexyloctyl hexoxysuccinate.

A solution of sodium hexoxide was prepared as in the preceding experiment, except that only 2.0 moles of n-hexanol was used for the 0.1 g. atom of sodium. To this solution, weighing 206 g., 172 g. of diethyl maleate (1.0 mole) was added and the temperature maintained at 50-60 C. for 4 hours. A mixture of 130 g. (1.0 mole) isooctyl alcohol, 204 g. (2.0 moles) 2-ethylbutanol, and 500 ml. of toluene was added. The mixture was distilled at atmospheric pressure to C., acetic acid was added to neutralize, and carbon was added to decolorize. This was distilled finally under a vacuum of 5.0 mm. of

mercury to a maximum pot temperature of 195 C. The bottoms, weighing 386 g., was filtered.

EXAMPLE V In this example, di-oxo decyl methoxy-succinate was prepared.

In this example, mixed n-octyl oxo decyl methoxysuccinate was prepared.

Two hundred grams of diethyl methoxysuccinate was mixed with 234 g. n-octyl alcohol, 284 g. oxo decyl alcohol, 600 ml. toluene, and 10.8 g. sodium methylate. The two alcohols were present in equimolar proportions. This mixture was distilled at atmospheric pressure until all the toluene had been removed, and 32 g. acetic acid was added to neutralize. The neutralized mixture was washed three times with water and distilled at atmospheric pressure to a pot temperature of C. Thirty grams decolorizing carbon was added, and it was then distilled at a pressure of 3.5 mm. of mercury to a maximum pot temperature of 212 C. The weight of the bottoms was 361 g.

EXAMPLE VII The preparation of 2-ethylhexyl, isooctyl n-butylthiosuccinic acid is illustrated by this example.

Ninety-nine grams (1.1 g. 'mole) of n-butyl mercaptan under nitrogen was reacted with 2.3 g. sodium (0.1 g. atom) to prepare a solution of sodium n-butyl mercaptide in n-butyl mercaptan. When the reaction was complete, there was slowly added 170 g. diethyl maleate (1.0 g. mole). The mixture was held at 5060 C. for several hours. Then there was added 325 g. 2-ethylhexanol and 325 g. isooctyl alcohol and 300 ml. toluene. The mixture was distilled to a pot temperature of 200 C. at atmospheric pressure, which removed all components boiling below C alcohols. The material was then given additional workings as in the above examples to give the 2-ethylhexyl, isooctyl n-butyl thiosuccinic acid.

The following table provides additional analytical data on the compositions of the above examples as well as other compositions illustrative of the invention. The physical properties of the esters are also given where appropriate. It will be noted that in some of the examples, the esters were obtained in pure form whereas in others the esters are crude products containing the esters and other unidentified materials of comparable boiling point.

The above oil was heated in the coking test for 8 hours at 700 F. and gave 2749 mg. of coke. A commercial gas turbine lubricant blended with the same additives but consisting of a di-2-ethylhexyl sebacate for the base fluid yields 3600 mg. of coke.

Equivalent weight Viscosit cs. Ex. N 0. R R R Alkoxy- Neut y Visc. F.P.,

, succinate, N 0. Index F. Found Theory percent 100 F. 210 F.

n-Octyl n-Octyl Methyl 190 186 16.83 3. 963 155 +45 2-ethylhexyl 2-ethylhexyl 2-ethylhexyl 198 235 62 20. 52 3. 981 100 fi5P yl n-Hexyl n-Hexyl 158 193 69 9. 945 2. 713 125 +5 yl }2-ethylbuty1 do 59 12 81 3.088 113 -P 0x0 decyL. OX0 decyL- Methyl. 100 31.05 4. 427 19 40 n-Octyl do .-do w 100 15. 52 3. 52 120 -P 2 ethylhexyl Isooctyl n-Butylthio 1 32 75. 5 9.83 116 an-Octyl 0x0 decyL. Methyl 100 14. 92 3.45 123 P rt-Oct -.do do 13.44 3.17 112 -80P 0x0 decyl 100 22. 46 4.404 65P n-Deeyl 100 16. 51 3. 866 +20 1 Thio.

From the physical characteristics of the illustrative dialkyl diesters of alkoxysuccinic acids and alkylthiosuccinic acids in the above examples, it is readily seen that the compounds of the invention possess excellent viscositytemperature properties as well as other desirable physical characteristics which make them particularly suitable as synthetic lubricants. They have unusually low freezing points compared to other types of dialkyl diesters of dibasic acids. The esters also have unusually high viscosity indexes. The dialkyl diesters of methoxysuccinic acids in which one alkyl group is straight-chain and the other branched-chain are particularly outstanding with respect to the combination of low freezing point and unusually high viscosity index.

The high temperature stability of the dialkyl diesters of alkoxysuccinic acid according to the invention was determined by heating the compounds at elevated temperatures in oxygen-containing atmosphere and noting the change, if any. In such a test, di-n-octyl n-octyloxysuccinate was heated for 48 hours at 392 E. An examination of the physical properties of the ester after heating showed essentially no change.

In further illustration of a particular embodiment of the present invention, a typical gas turbine lubricant was prepared from an illustrative ester and subjected to a modified coking test as described in government specifications Mil-L-7807c and Mil-D2536. The test was conducted in the same manner .as described in the specifications except that the temperature of the heated plate was held at 700 F. instead of 600 F. in order to make the test more severe. This gas turbine lubricant was also compared with a commercial gas turbine lubricant in the test. The composition of the experimental lubricant is as follows:

The above tests show that illustrative dialkyl diesters of alkoxysuccinic acids according to the present invention have excellent high temperature properties which make them ideally suited as base lubricants in the preparation of gas turbine lubricating oils.

I claim:

1. A gas turbine lubricating oil composition consisting essentially of a major proportion of a dialkyl diester of methoxysuccinic acid in which one of the ester-linked alkyl groups is n-octyl and the other ester-linked alkyl group is a branched chain decyl, a minor proportion of phenothiazine sufiicient to inhibit oxidation, a minor proportion of tricresyl phosphate sufficient to improve wear inhibition and a minor proportion of octadecylamine salt of dodecylphosphoric acid sufiicient to improve the extreme pressure characteristics.

2. A gas turbine lubricating oil composition consisting essentially of a major proportion of a dialkyl diester of methoxysuccinic acid in which one of the ester-linked alkyl groups is n-octyl and the other ester-linked alkyl group is a branched chain decyl, from 0.2 to 5% by weight of phenothiazine, from 0.5 to 5% by weight of tricresyl phosphate and from 0.05 to 1% by weight of octadecylamine salt of dodecylphosphoric acid.

References Cited by the Examiner UNITED STATES PATENTS 2,559,521 7/ 1951 Smith et a1. 252-565 2,801,968 8/1957 Furby et a1. 25-232.5 2,820,014 1/1958 Hartley et a1 252-56 2,837,562 '6/1958 M'atuszak et a1 260485 DANIEL E. WYMAN, Primary Examiner. 

1. A GAS TURBINE LUBRICATING OIL COMPOSITION CONSISTING ESSENTIALLY OF A MAJOR PROPORTION OF A DIALKYL DIESTER OF METHOXYSUCCINIC ACID IN WHICH ONE OF THE ESTER-LINKED ALKYL GROUPS IS N-OCTYL AND THE OTHER ESTER-LINKED ALKYL GROUP IS A BRANCHED CHAIN DECYL, A MINOR PROPORTION OF PHENOTHIAZINE SUFFICIENT TO INHIBIT OXIDATION, A MINOR PROPORTION OF TRICRESYL PHOSPHATE SUFFICIENT TO IMPROVE WEAR INHIBITION AND A MINOR PROPORTION OF OCTADECYLAMINE SALT OF DODECYLPHOSPHORIC ACID SUFFICIENT TO IMPROVE THE EXTREME PRESSURE CHARACTERISTICS. 